Methods and apparatus for monitoring at least one sensor utilized in a vehicle are known in the existing art in many modifications.
German Unexamined Patent Application No. 44 46 535 discloses a circuit arrangement for amplitude measurement in which the amplitude of the output signal of an inductive sensor is measured. The circuit arrangement includes two measurement branches, to each of which the output signal of the inductive sensor is sent. The first measurement branch determines a voltage value corresponding to the peak value of the voltage. The task of the second measurement branch is to make available, based on the output signal of the inductive sensor, switchover conditions for the components contained in the first measurement branch.
The first measurement branch is implemented as a series circuit consisting of a first amplifier, a peak value rectifier downstream from it, a second amplifier downstream from that, and a downstream collection and holding circuit. The second measurement branch is made up of a comparator and two multivibrator circuits, in particular flip-flops, downstream from it. The signals needed to influence the first measurement branch are generated by means of these multivibrator circuits. The collecting and holding circuit is influenced on the basis of the first multivibrator circuit, and the peak value rectifier is triggered by the signal generated by the second multivibrator circuit.
With the circuit arrangement indicated, it is possible to determine the quality of the output signal generated by the inductive sensor in a wide range of frequencies and voltage, by means of a plausibility check. The plausibility check is accomplished by the fact that the voltage values generated in the first measurement branch are compared with plausible voltage values.
A method for monitoring rotation speed sensors is known from German Unexamined Patent Application No. 42 11 622. This is, in particular, a method for monitoring inductive rotation speed sensors. In order to monitor these, a DC voltage signal is overlaid on each of the inductive rotation speed sensors. At the same time, one terminal of the inductive rotation speed sensor is connected to two lines which connect to a microprocessor. Using the first line, the voltage level present at the terminal of the inductive rotation speed sensor can be analyzed by means of the microprocessor. The microprocessor can deliberately modify that voltage level via the second line.
This method can be used to detect essentially two faults. The first fault--the presence of a line break or a short circuit to the connecting line--is detected by the fact that the voltage level sent via the first line to the microprocessor changes. This first fault can, however, be detected only if the voltage level has not been deliberately changed by the microprocessor via the second line. If a first fault of this kind is detected, the system can, for example, be switched off.
Since it is common for more than one inductive rotation speed sensor to be utilized in a vehicle, a second fault--a short circuit between the rotation speed sensors or their connecting lines--can also occur. If all the inductive rotation speed sensors are connected as described above, a second fault of this kind can be detected by means of the indicated method. For this, the voltage level of a first inductive rotation speed sensor is deliberately modified, via its second line, by the microprocessor. If a short circuit is present between two rotation speed sensors or their connecting lines, the voltage level of the second inductive rotation speed sensor will also change as a result of the change in voltage level at the first inductive rotation speed sensor. This change in voltage level at the second inductive rotation speed sensor can be recognized via its second line by the microprocessor. Monitoring of the first inductive rotation speed sensor via the first line must be discontinued while the arrangement is being checked for a second fault.
The article "New Alternative Solutions for Magnetoresistive Rotation Speed Sensors in Motor Vehicles" (Neue, alternative Losungen fur Drehzahlsensoren im Kraftfahrzeug auf magnetoresistiver Basis, VDI-Berichte No. 509, 1984, pp. 263-268), and the article "Integrated Hall-effect Sensors for Detecting Position and Rotation Speed" (Integrierte Hall-Effekt-Sensoren zur Positions- und Drehzahlerkennung, elektronik industrie 7, 1995, pp. 29-3), both indicate sensors for use in motor vehicles in systems for controlling or regulating antilock braking systems, automatic slip systems, and the engine and transmission, with which rotary motions can be detected.
It is an object of the present invention to improve the monitoring of sensors utilized in vehicles, in particular of inductive sensors.